A conventional heat pump system having a hot-water facility for use in a building includes a heat pump, a room air conditioning unit disposed within each room, a circulating pump for supplying each room air conditioning unit with heating and cooling medium, a backup boiler for providing an supplementary source of heat in the air heating operation, a hot-water supply tank, a hot-water supply boiler and a hot-water circulating pump. A preheating heat exchanger is disposed in the hot-water supply tank.
Referring to FIG. 1, a conventional control device for a heat pump system having a hot-water supply facility is shown. The control device includes an ambient air temperature sensor S1, an ambient air moisture sensor S2, a hot-water supply temperature sensor S3, a hot-water supply switch SW for detecting the presence or absence of a hot-water supply, and an operation circuit 20 for selecting an operation mode, i.e., the cooling air mode, the cooling air and hot-water supply mode, the heating air mode, the hot-water supply mode, or the heating air and hot-water supply mode, in accordance with output signals from sensors S1, S2, S3 and switch SW. The device also includes a control circuit 30 for operating the system components in accordance with the mode selected by operation circuit 20.
To explain further, with reference to FIG. 2, in the cooling air mode, heating and cooling medium contained in tank 16 is cooled during operation of heat pump 1, and is distributed to room air conditioning unit 2 through conduit 17. There, the cooled medium absorbs the surrounding heat so that cooled air is supplied to the interior of the room. In addition, in the cooling air and hot-water supply mode, and in the hot-water supply mode, water in hot water supply tank 6 is heated with preheat heat exchangers 4 and 5, resepctively, during operation of the heat pump, and is then further heated by operating hot-water supply boiler 7.
In the heating mode, heat pump 1 is operated to heat the medium contained in tank 16, and if additional heat is required, backup boiler 3 is operated to further heat the medium. The heated medium is then distributed to room air conditioning unit 2 where the heat is extracted so that heated air supplied to the interior of the room. In addition, in the heating air and hot water supply mode, the water in hot-water supply tank 6 is heated by operating hot-water supply boiler 7.
In the described system, heat pump 1 is driven by an electric motor (not shown), and boilers 3 and 7 both use oil as an energy source. In the conventional arrangement, the control device is designed to use either the heat pump or one of the boilers during the heating mode and the hot-water supply mode depending upon the condition of the ambient air, e.g., the air temperature and moisture level. However, no provision is made in the conventional system for automatically operating the heat pump or the boilers depending upon which uses the cheaper energy source. Further, it is impracticable and becomes very complicated to manually control this selection because the energy costs will vary depending upon the selected air or water temperature, the operation time, and the energy unit price.